Question

Let \[ \vec a=i+2j+2k,\quad \vec b=2i-j+2k,\quad \vec c=2i+j+2k \] If \(\vec d\times \vec a=\vec b\times \vec a\) and \(\vec d\cdot \vec c=8\), then for \(\vec r=2i+2j+k\), find \(\vec d\cdot \vec r\)

• A. 3
• B. 4
• C. 5
• D. 30 \bigskip

Hint:

If cross products are equal, vectors differ by a multiple of the same vector.

Answer 1

The Correct Option is B